Conventionally in a wireless communication system of the cell scheme, synchronization of the transmission and reception timing is established between adjacent cells. More specifically, the transmission and reception timing between a wireless base station in a cell and a terminal device in that cell is made to match the transmission and reception timing between a wireless base station in an adjacent cell and a terminal device in that adjacent cell to suppress the interference between a wireless base station and a terminal device in the adjacent cell as well as the interference between terminal devices.
One approach to realize synchronization of the transmission and reception timing between such cells is to use a signal from a satellite including time information. As a typical example of a signal from a satellite including time information, a GPS (Global Positioning System) signal from a GPS satellite is known at the present time. Specifically, a GPS receiver for receiving a GPS signal from a GPS satellite is provided at each of wireless base stations to establish synchronization of the transmission and reception timing based on the common GPS signal.
A GPS module for generating a synchronizing signal of high accuracy is costly. One approach of reducing the cost is to share one independent GPS receiver among a plurality of wireless base stations. For example, Japanese Patent Laying-Open No. 2000-232688 (PTL 1) discloses a system having each base station integrated with a GPS receiver. In this system, the GPS receiver receives a GPS signal from a GPS satellite, and the GPS signal (reference signal) is employed as a common time basis among the plurality of wireless base stations.
In order to monitor the state of the GPS receiver, an EMS (Element Management System) is installed. A conventional EMS is a management server for monitoring and controlling, based on state information representing a normal state or an error state transmitted from the GPS receiver incorporated in a wireless base station. The EMS monitors and controls a wireless base station based on SNMP (Simple Network Management Protocol) that is a standard management protocol.